Switching apparatus for selectively and sequentially operating two rows of lamps with lock-out means therebetween

ABSTRACT

A switching device for sequentially operating two or more rows of lamps. An elongated light conductor is arranged between the two rows of lamps so that the light from a lamp of the first row and the light from a corresponding lamp of the second row emanate from the same given surface area of the light conductor. Cross connections are provided between switching elements connected in first and second circuits providing sequential operation of said first and second rows of lamps, respectively, so that when a lamp of one row is ignited, the corresponding lamp of the other row cannot be ignited simultaneously.

United States Patent 1 Bruinsma 1 Jan. 9, 1973 [5 1 SWITCHING APPARATUSFOR [56] References Cited SELECTIVELY AND SEQUENTIALLY UNITED STATESPATENTS OPERATING TWO ROWS OF LAMPS Y WITH LOCK OUT MEANS g/1952 Peteret a1. ......340/380 /l954 Rothman ..340/380 THEREBETWEEN 3,225,34212/1965 Clark ....340/l68 s Inventor: Anne Hendrik Bruinsma, Emmasin3,568,177 3/1971 Hasler ..340/324 R l Emdboven Netherlands PrimaryExaminer-John W. Caldwell [73] Assignee: U.S. Philips Corporation, New 1Assistant Examiner-Marshall M. Curtis York, NY. Attorney-Frank R.Trifari [21] Appl' 77300 A switching device for sequentially operatingtwo or more rows of lamps. An elongated light conductor is [30] ForeignApplication Priority Data arranged between the two rows of lamps so thatthe light from a lamp of the first row and the light from a Oct. 5, 1970Netherlands ..69l5254 corresponding lamp of the second row emanate fromthe same given surface area of the light conductor. [52] U.S. Cl...340/379, 340/168 S, 340/380 Cross connections are provided betweenswitching {51 Int. Cl. ..G08b 5/36 elements connected in first andsecond circuits provid- [58] Field of Search ..340/378, 379, 380, 324,325, ing sequential operation of said first and second rows of lamps,respectively, so that when a lamp of one row is ignited, thecorresponding lamp of the other row cannot be ignited simultaneously.

13 Claims, 3 Drawing Figures PMENTEDJM 9197s 3.710.379

sum 1 OF 2 IXYEX'I'OR.

ANNE H. BRUINSMA K rpm/QM- AGENT PATENTEUJAH 9197a 3.710.379

' sum 2 OF 2 Fig.3

IXVEXTOR.

ANNE H. BRUINSMA SWITCHING APPARATUS FOR SELECTIVELY AND SEQUENTIALLYOPERATING TWO ROWS I OF LAMPS WITI-I LOCK-OUT MEANS TIIEREBETWEEN Thisinvention relates to a switching apparatus for a moving light displaycomprising at least two rows of lamps. Associated with and adjacent toeach lamp of the first row is a lamp of the second row. Each lamp ofeach row is connected in series with a switching element so that amoving light picture is obtainable with each of the rows of lamps.

A known switching apparatus of the kind set forth is employed, forexample, for a luminous newspaper. In

this case a panel having a great number of lamps is used on which movingtexts are rendered visible. Such a device is described, for example, inDutch Pat. application No. 6,818,241. The information display systemdisclosed in said Patent application comprises a panel having a numberof lamps arranged in rows and columns. The character displayed movesfrom right to apparatus in which the light from two co-ordinated lampsapparently emanates from the same place. The apparatus includes meansfor preventing the simultaneous emission of light from the twoco-ordinated lamps. Such a switching apparatus serves to provide morevariation in a moving light display.

A switching apparatus, according to the invention,

for a moving light, display comprises at least two rows I of lamps, inwhich adjacent each lamp of the first row there is associated a lamp inthe second row, and each lamp of each row is connected in series with aswitching element so that a moving light picture can be obtained by eachof the rows of lamps. The invention is characterized in that light froma lamp of the first row is conducted through a light conductor to asurface thereof and emanates from said surface. The light from theassociated lamp of the second row also is conducted through the lightconductor and emanates from the same surface of the lightconductor.Electric cross connections are provided between elements of the circuitsof the first and second rows of lamps so that in the ignited state of alamp a voltage is produced across a cross connection of a magnitude andpolarity to hold the switching element of the lamp associated with theignited lamp in the non-conducting state.

Such a switching apparatus (according to the invention) has theadvantage that it can be indicated how two flow quantities pass alongthe same track and in the same direction. This may apply to imitationsof traffic flows (for example, of cars).

The light from the first row of lamps may have a spectral compositiondiffering from that of the other row of lamps. Moreover, between thefirst row of lamps and the light conductor a color filter may bearranged or different color filters may be provided between the two rowsof lamps and the light conductor. The first row of lamps may, forexample, radiate green light from the light conductor, whereas thesecond row of lamps radiates red light. In a device according to theinvention, if, for example, at one place on the light conductor redlight is radiated, the adjacent green lamp cannot radiatesimultaneously. If desired, a rapidly moving green signal may be causedto pass bya slowly moving red signal.

In a particular embodiment of a switching apparatus in accordance withthe invention the different colors of I each of the rows of lamps arecombined with such circuitries of each of the rows of lamps that themoving light of one row does not skip a lamp.

Such a preferred embodiment has the advantage that it is simply possibleto imitate a situation in which a given flow cannot be passed by afurther flow, but can only overtake it. Overtaking is to denote hereinadiminution of the relative distance. After overtaking the speed of thenext flow is equal to that of the leading flow.

An example of flows running with equal speeds one after the other isgiven by the situation occurring in an oil pipeline. Different qualitiesof oil maybe pumped one after the other through the line. Such asituation can be satisfactorily displayed by a switchingapparatus inaccordance with the invention.

For each pair of co-ordinated lamps one short, e.g.

cork'shaped light conductor may be provided.

Moreover, a number of lamps of one row and a number of lamps of theother row may together radiate light into one light conductor.

In a further preferred embodimentof the switching apparatus inaccordance with the invention the light conductor is elongated andafirst row of lamps is arranged on one side of the light conductor and asecond row of lamps on a second side thereof, whereas a third side ofthe light conductor is formed by a collection of surfaces from which thelight emanates. This is a very practical embodiment of a switchingapparatus in ac cordance with the invention. It does not require a largenumber of light conductors; a single long conductor is 1 sufficient,which imitates, for example, a pipeline in more realistic fashion.

The switching elements jmay be relays. Said cross connections may becoupled with the energizing windings of said relays.

In a further preferred embodimentof the switching apparatus inaccordance with the invention the switching elements in series with thelamps are formed by transistors. The electric cross connection iscoupled on one side with the connection of a lamp to the associatedtransistor and on the other side with the base of the transistor of thelamp associated with the firstmentioned lamp. l

The latter embodiment may advantageously be ar- I ranged so that eachelectric cross connection includes a:

Referring to FIG. 1, reference numeral 1 designates a long lightconductor of a transparent synthetic resin, passed through a panel 2. Onthe lower side of said light conductor three rows of lamps are arranged,i.e. 3, 4 and 5, respectively. The lamps 3 are green, the lamps 4 redand the lamps 5 yellow. When the first green lamp is ignited, the firstsurface segment (1a) of the light conductor (1) will irradiate greenlight. If, however, instead of the first green lamp the first red lampof row 4 is ignited, the surface la will irradiate red light. When thefirst lamp of row 5 is ignited, the surface 1a will in radiate yellowlight. The electric coupling between the circuits for the rows 3, 4 and5, to be described hereinafter is arranged so that the surface 1a cannever irradiate a mixture of the said three basic colors.

In FIG. 2 the same reference numerals are used as in FIG. 1. The row 4is the lowermost row of lamps.

. FIG. 3 can be divided into three parts a, b and c. The part a relatesto the circuit for the green lamps of row 3 of FIG. 1, part b of FIG. 3to the circuit for the red lamps of row 4 of FIG. 1 and part c of FIG. 3to the circuit for the yellow lamps of FIG. 1.

The parts a, b and c of FIG. 3 are substantially identical. These threeparts are interconnected by transverse (cross) connections, which willbe described hereinafter. First the circuit part a of FIG. 3 will bedescribed in detail. The part a of FIG. 3 comprises three uninterruptedconductors 20, 21 and 22. Con- .ductor is connected to the positiveterminal of a voltage source, not shown. The conductor 21 is connectedto a negative terminal thereof. The conductor 22 is coupled with avariable control-voltage of negative potential.

One end of a capacitor 23 is connected to the uninterrupted conductor20. The other end of said capacitor 23 is connected through a resistor24 to the uninterrupted conductor 22. The capacitor 23 is shunted by acircuit including a switch 25. The. switch 25 is a bipolar switch forreasons to be referred to hereinafter. The connection between capacitor23 and resistor 24 has connected to it a Zener diode 26. The other endof said Zener diode is connected to a resistor 27 and to the base of atransistor 28. The other end of the resistor 27 and the emitter of thetransistor 28 are connected to the uninterrupted conductor 20. Thecollector of the transistor 28 is connected via a resistor 29 to theunin- .terrupted conductor 21. A junction point between the collector oftransistor 28 and the resistor 29 is designated by reference numeral 30.This point 30 has connected to it a contact of the switch 25 and, inaddition, a Zener diode 31. The other end of the Zener diode 31 isconnected to a resistor 32 and to the base of a transistor 33. The otherend of the resistor 32 and the emitter of the transistor 33 areconnected to the uninterrupted line 20. The collector of the transistor33 is connected through an incandescent lamp 34 to the uninterruptedconnecting line 21. A junction of the transistor 33 and the lamp 34 isconnected to a diode 35. The other end of the diode 35 is connected to acapacitor 36. The opposite electrode of capacitor 36 is connected to thepositive terminal via the conductor 20. The diode 35 is also connectedto a resistor 37, the other end of which is connected to theuninterrupted conductor 22. A junction of the transistor 33 and thediode 35 is designated by reference numeral 38. The

I junction 38 is connected via a diode 39 and a switch 25b to a point30b of the circuit part b of FIG. 3. The point 38 is furthermoreconnected via a diode 40 and a switch 250 to a point 300 of thecircuit-part c of FIG. 3.

Beyond elements 36 and 37 the circuit is repeated in the part a and theconnection of capacitor 36 and resistor 37 is again coupled to a Zenerdiode 26, etc.

The circuit part b(c) of FIG. 3 is identical to the circuit part a. Inthe part b the reference numerals are the same as in part a, but theyhave in addition a reference letter b, whereas in the part c they havean additional c. The transverse connections of part b(c) to the furthercircuit elements are also identical to those of part a of FIG. 3. Theconductors 20, 20b and 200 have the same potentials. The conductor 21,21b and 21c also have the same potentials.

This circuit operates as follows.

It is assumed that at a given instant capacitor 23 is charged. Thismeans that its electrode facing the conductor 22 is at a negativepotential. The diode 26 will then pass current in the reverse direction.A current then passes through the resistor 27 so that at the base oftransistor 28 a potential occurs such that this transistor becomesconducting. Point 30 will thus be at such a potential that the voltageacross the Zener diode 31 is When capacitor 23 is discharged by closingthe switch 25, the current through the diode 26 is interrupted. Thetransistor 28 thus becomes non-conducting. The Zener diode 31 thenreceives a current in the reverse direction. This current causes thetransistor 33' to become conducting, which results in the ignition ofthe lamp 34. The conductive state of the transistor 33 will result,moreover, via diode 39 and switch 25b, in a positive voltage at point30b of the circuit part b. The transistor 33b of thepart b of FIG. 3 isthen non-conducting and at this instant the lamp 34b is extinguished. Ina similar manner via point 38 and the diode 40 and via switch 250 theconductive state of transistor 33 results in a positive voltage at point30c. The result is that the transistor 330 is non-conducting so that thelamp 340 also is extinguished. The lamps 34b and 340 associated with thelamp 34 are therefore not ignited when the lamp 34 is ignited. A thirdconsequence of the conductive state of transistor 33 is that the chargedcapacitor 36 is discharged across the transistor 33 and the diode 35. Inthe discharge state no current can flow through the Zener diode 26' sothat the transistor 28' is non-conducting. In a manner similar to thatfor the circuit elements 26 to 34, the lamp 34' will ignite. In asimilar manner the lamp 34" ignites in turn, etc.

Since the switch 25 is actuated only for a short time, the capacitor 23is charged after some time via the resistor 24. This charged stateresults in the extinction of the lamp 34. The lower the voltagedifference between the conductors 20 and 22, the later will extinguishthe lamp 34. The situation is then as follows: When the switch 25 isactuated for a short time, first lamp 34 will ignite, then lamp 34',then 34" etc., the lamps 34, 34', etc. extinguishing at a slower ratethan the ignition rate. The slower rate of extinction of the lamps 34,34, etc.

than the rate of ignition thereof is due to the fact that the capacitor(for example, 36) is charged via the resistor (37) by means of a currentwhich is lower than the discharge current of said capacitor (36) whichflows, in the conductive state of the transistor (33), through saidtransistor and the diode (35). If desired, a control-voltage 22-20 maybe chosen, of such low value is chosen, that the first lamp (34) is notextinguished until the last lamp of the circuit-part a has ignited. In asimilar manner to that described for the lamp 34, the lamps 34b and 34'cwill be cut off when the lamp 34' has ignited. So when the lamp 34' isignited, the other associated lamps 34' are extinguished. Conversely,when a lamp in the part b is ignited, the coupled lamps of the parts aand c are extinguished, etc. If a color signal" is already present inone of the circuit parts, the rate of ignition of the subsequentlyigniting lamps in one of the further circuits parts will be limited bythe rate of extinction of the said color signal.

As stated .above the switch is a bipolar switch. When it occupies theposition in which capacitor 23 is shunted, the cross connections via thediode 40b and 400 of the parts b and 0, respectively, to. the part a areinterrupted. So in the circuit described the actuation of the switch 25in the part a causes the parts b and c to release the blocking action onthe lamp 34. Thus a signal can pass through the part a. The ignited lampblocks the coupled lamps of the other circuit parts. This appliessimilarly to the switches 25b and 25c.

The apparatus described above is highly appropriate for displaying thesubsequent conveyance of different qualities of oil through onepipeline. It is assumed that a first oil quality is indicated by thegreen color of the lamps 34, 34', etc. and a second oil quality isindicated by the red color of the lamps 34b, 34b, etc and finally athird oil quality is indicated by the yellow color of the lamps 34c,34c, etc. When switch 25 is depressed for a short time, the entry of thefirst oil quality in the pipeline is imitated by a green light in thedevice of FIG. 1. When the control-voltage 22-20 is adjusted to a lowvalue, the whole pipeline may, if desired, be filled with green light..When the switch 25b is actuated for a short time, a second oil quality(red light) flows into the line etc.. If desired, by actuating theswitch 25, a

third oil quality can be introduced into the pipeline, which is pumpedin after the first two qualities. Subsequently, one of the switches 25bor 25 again may be actuated, etc.

At the end of the circuit part a an energizing winding of a relay may beprovided for a short-time actuation of the switch 25 at the input. Thusa signal once started in the circuit part a moves from left to right andis re-introduced at the input of circuit part a.-A similar provision maybe carried out for the circuit part b and the circuit part c. Then themoving light picture will be constantly repeated.

At the output of the circuit part a a memory element may be provided sothat a signal arriving at the output of the circuit part a isre-introduced with some time lag at the capacitor 23.

If desired, a cut-off member may be provided, which, when a lamp isignited, keeps extinguished a lamp in a further row, and the lastmentioned lamp is located before the lamp joined to the first-mentionedlamp.

In a practical embodiment of the circuit of FIG. 3 the resistor 24 had avalue of about. 47 kOhms and the capacitor 23 had a capacitance of about32 'uF. The resistor 27 had a valueof about 5.6 kOhms and the resistor29 a value of about 1.2 kOhms. The Zener diodes 26 and 31 had a reversevoltage of about 4.7 V. The voltage between the conductor 20 to 21 wasabout 12 V and that between 22 and 20 could be varied between 9 V and 30V.

By means of a device in accordance with the invention, other flowquantities such as the flow of money and/or goods may be displayed. ifdesired, the lightpearance of a moving spot of light comprising, two

rows of lamps arranged so that there is present adjacent each lamp ofthe first row a lamp of the second row, a circuit for each row of lampsincluding means connecting each lamp of each row in series with acontrolled switching element, means for sequentially operating saidswitching elements to produce said moving spot of light for each of therows of lamps, a light conductor optically coupled to said two rows oflamps so that light from a lamp of the first row is conducted via saidlight conductor to a given surface area thereof and emanates therefrom,from which given surface area the light from the lamp adjacent theretoof the second row 'of lamps emanates, and electric cross connectionmeans pro vided between switching elements of the circuits of the firstand second rows of lamps so that, when a lamp is ignited, a voltage iscoupled across a corresponding cross connection of a magnitude andpolarity to hold the switching element of the lamp adjacent to theignited lamp in the non-conducting state.

2. A switching apparatus as claimed in claim 1 in which the operatingmeans for the circuits of the lamps of each of the two rows are arrangedso that the lamps are operated in sequence to produce said moving spotof light for each row, characterized in that the light emanating fromsaid given surface and originating from a lamp of the first row has adifferent color than that emanating from said given surface andoriginating from a lamp of the second row.

3. A switching apparatus as claimed in claim 2 in which the lightconductor comprises an elongated member with the first row of lampsarranged on one side of the light conductor and the second row of lampsarranged on a further side of the light conductor, a third side of thelight conductor being formed by a collection of said given surface areasto form a surface from which light emanates.

4. A switching apparatus as claimed in claim 1 wherein each of theswitching elements in series with the lamps comprises a transistor andwherein an electric cross connection includes a'diode coupled at one endto the junction of a lamp and its associated series transistor of thefirst row of lamps and at the other end to the base of the transistor inseries with the corresponding lamp of the second row of lamps.

5. A switching apparatus as claimed in claim 1 wherein each of saidswitching elements comprises a transistor and wherein each electriccross connection going from the first row of lamps includes a diodewhose pass direction points towards the base of the' transistor inseries with the adjacent lamp of the second row of lamps.

6. A system for sequentially operating a plurality of lamps comprising,a light conductor, first and second rows of lamps optically coupled tothe light conductor so that for each lamp of the first row there is acorresponding lamp of the second row arranged so that said lightconductor emits light from said corresponding lamps at correspondinggiven areas of said light conductor, a first plurality of controlledswitching elements connected in a first circuit with said first row oflamps to form a plurality of separate stages adapted to be operated insequence, a second plurality of controlled switching elements connectedin a second circuit with said second row oflamps to form a plurality ofseparate stages adapted to be operated in sequence, each of said firstand second circuits including means for selectively energizing the firststage in the sequence and means intercoupling the stages so thatoperation of the first stage triggers the second stage into operation,the second stage in turn triggers a third stage, and so on, and aplurality of electric cross connections each of which couples aswitching element of one circuit to the corresponding switching elementof the other circuit so that, when a lamp of one circuit is ignited, acontrol voltage is coupled via its associated cross connection to thecorresponding switching element of the other circuit with a magnitudeand polarity to hold the corresponding stage of said other circuit andits lamp inoperative.

7. A system as claimed in claim 6 wherein each of said cross connectionsincludes a unidirectional current conducting element. 7

8. A system as claimed in claim 6 wherein each of said stages includes alamp and a switching element connected in series and the first stageincludes an RC timing circuit and a voltage breakdown element couplingsaid RC circuit to a control electrode of the switching element of saidfirst stage.

9. A system as claimed in claim 8 further comprising an RC timingcircuit connected in each stage and a voltage breakdown element couplingeach RC timing circuit to the control electrode of the respectiveswitching element for that stage.

10, A system as claimed in claim 9 wherein said stage intercouplingmeans comprises a diode connected between a switching element of onestage and the capacitor of the RC timing circuit of the next stage inthe sequence, said diode being poled so as to provide a discharge pathfor said capacitor via said one stage switching element.

11. A system as claimed in claim 7 wherein said selective energizingmeans comprises a switching device connected in circuit so as toselectively open and close the cross connections between the first stageswitching elements of said first and second circuits.

12. A system as claimed in claim 8 wherein said selective energizingmeans comprises a switching device connected in circuit so as toselectively open and close the cross connections between the first stageswitching elements of said first and second circuits and simultaneouslyto close and open, respectively, a discharge path for the capacitor ofsaid first stage RC timing circuit.

13. A system as claimed in cla1m 6 wherein the light conductor comprisesan elongate transparent member with a hexagonal cross-section thatdefines a first pair of parallel surfaces one of which includes saidgiven areas and a second pair of parallel surfaces orthogonal to andintersecting said one surface, and fifth-and sixth surfaces making anobtuse angle with the second pair of parallel surfaces, said first andsecond rows of lamps being arranged adjacent to said fifth and sixthsurfaces, respectively.

1. A switching apparatus for producing the appearance of a moving spotof light comprising, two rows of lamps arranged so that there is presentadjacent each lamp of the first row a lamp of the second row, a circuitfor each row of lamps including means connecting each lamp of each rowin series with a controlled switching element, means for sequentiallyoperating said switching elements to produce said moving spot of lightfor each of the rows of lamps, a light conductor optically coupled tosaid two rows of lamps so that light from a lamp of the fiRst row isconducted via said light conductor to a given surface area thereof andemanates therefrom, from which given surface area the light from thelamp adjacent thereto of the second row of lamps emanates, and electriccross connection means provided between switching elements of thecircuits of the first and second rows of lamps so that, when a lamp isignited, a voltage is coupled across a corresponding cross connection ofa magnitude and polarity to hold the switching element of the lampadjacent to the ignited lamp in the non-conducting state.
 2. A switchingapparatus as claimed in claim 1 in which the operating means for thecircuits of the lamps of each of the two rows are arranged so that thelamps are operated in sequence to produce said moving spot of light foreach row, characterized in that the light emanating from said givensurface and originating from a lamp of the first row has a differentcolor than that emanating from said given surface and originating from alamp of the second row.
 3. A switching apparatus as claimed in claim 2in which the light conductor comprises an elongated member with thefirst row of lamps arranged on one side of the light conductor and thesecond row of lamps arranged on a further side of the light conductor, athird side of the light conductor being formed by a collection of saidgiven surface areas to form a surface from which light emanates.
 4. Aswitching apparatus as claimed in claim 1 wherein each of the switchingelements in series with the lamps comprises a transistor and wherein anelectric cross connection includes a diode coupled at one end to thejunction of a lamp and its associated series transistor of the first rowof lamps and at the other end to the base of the transistor in serieswith the corresponding lamp of the second row of lamps.
 5. A switchingapparatus as claimed in claim 1 wherein each of said switching elementscomprises a transistor and wherein each electric cross connection goingfrom the first row of lamps includes a diode whose pass direction pointstowards the base of the transistor in series with the adjacent lamp ofthe second row of lamps.
 6. A system for sequentially operating aplurality of lamps comprising, a light conductor, first and second rowsof lamps optically coupled to the light conductor so that for each lampof the first row there is a corresponding lamp of the second rowarranged so that said light conductor emits light from saidcorresponding lamps at corresponding given areas of said lightconductor, a first plurality of controlled switching elements connectedin a first circuit with said first row of lamps to form a plurality ofseparate stages adapted to be operated in sequence, a second pluralityof controlled switching elements connected in a second circuit with saidsecond row of lamps to form a plurality of separate stages adapted to beoperated in sequence, each of said first and second circuits includingmeans for selectively energizing the first stage in the sequence andmeans intercoupling the stages so that operation of the first stagetriggers the second stage into operation, the second stage in turntriggers a third stage, and so on, and a plurality of electric crossconnections each of which couples a switching element of one circuit tothe corresponding switching element of the other circuit so that, when alamp of one circuit is ignited, a control voltage is coupled via itsassociated cross connection to the corresponding switching element ofthe other circuit with a magnitude and polarity to hold thecorresponding stage of said other circuit and its lamp inoperative.
 7. Asystem as claimed in claim 6 wherein each of said cross connectionsincludes a unidirectional current conducting element.
 8. A system asclaimed in claim 6 wherein each of said stages includes a lamp and aswitching element connected in series and the first stage includes an RCtiming circuit and a voltage breakdown element coupling said RC circuitto a control electroDe of the switching element of said first stage. 9.A system as claimed in claim 8 further comprising an RC timing circuitconnected in each stage and a voltage breakdown element coupling each RCtiming circuit to the control electrode of the respective switchingelement for that stage.
 10. A system as claimed in claim 9 wherein saidstage intercoupling means comprises a diode connected between aswitching element of one stage and the capacitor of the RC timingcircuit of the next stage in the sequence, said diode being poled so asto provide a discharge path for said capacitor via said one stageswitching element.
 11. A system as claimed in claim 7 wherein saidselective energizing means comprises a switching device connected incircuit so as to selectively open and close the cross connectionsbetween the first stage switching elements of said first and secondcircuits.
 12. A system as claimed in claim 8 wherein said selectiveenergizing means comprises a switching device connected in circuit so asto selectively open and close the cross connections between the firststage switching elements of said first and second circuits andsimultaneously to close and open, respectively, a discharge path for thecapacitor of said first stage RC timing circuit.
 13. A system as claimedin claim 6 wherein the light conductor comprises an elongate transparentmember with a hexagonal cross-section that defines a first pair ofparallel surfaces one of which includes said given areas and a secondpair of parallel surfaces orthogonal to and intersecting said onesurface, and fifth and sixth surfaces making an obtuse angle with thesecond pair of parallel surfaces, said first and second rows of lampsbeing arranged adjacent to said fifth and sixth surfaces, respectively.